The present invention relates generally to nozzles for the atomization of fluids and, more particularly, to pressure atomizer nozzles used for atomizing fuel before injection into an internal combustion engine.
Automobile emissions are said to be the single greatest source of pollution in several cities across the country. Automobiles emit hydrocarbons, nitrogen oxides, carbon monoxide and carbon dioxide as a result of the combustion process. The Clean Air Act of 1970 and the 1990 Clean Air Act set national goals of clean and healthy air for all and established responsibilities for industry to reduce emissions from vehicles and other pollution sources. Standards set by the 1990 law limit automobile emissions to 0.25 grams per mile (gpm) non-methane hydrocarbons and 0.4 gpm nitrogen oxides. The standards are predicted to be further reduced by half in the year 2004.
It is expected that automobiles will continue to be powered by internal combustion engines for decades to come. As the world population continues to grow, and standards of living continue to rise, there will be an even greater demand for automobiles. The major challenge facing automobile manufacturers is to reduce undesirable emissions and improve fuel economy, thereby assuring the increased number of automobiles has a minimal impact on the environment. One method by which automobile manufacturers have attempted to improve fuel economy and reduce undesirable emissions is through direct fuel injection.
Generally, direct injection (DI) is the spraying of fuel under pressure through the nozzle of a fuel injector and into the combustion chamber of an internal combustion engine. By spraying a very precise amount of fuel in the form of atomized fuel particles into the combustion chamber, DI realizes a substantial reduction in undesirable emissions and an increase in fuel economy. Generally, the requirements for an efficient DI system are small fuel particle size, control of spray penetration, and control of the dispersion of the fuel particles within the combustion chamber.
The extent to which the injected fuel is atomized, as measured by the fuel particle size, is a critical factor in the efficiency of DI systems. Incompletely atomized fuel has large particle size whereas fuel that is substantially completely atomized has small particle size. Large fuel particles in DI systems create uncontrolled localized high concentrations of fuel within the combustion chamber. The large fuel particles evaporate into the combustion charge relatively slowly. Thus, an incomplete combustion process may result. In contrast, smaller fuel particles evaporate into the combustion charge relatively quickly, thereby promoting a homogenous mixture of fuel and air within the combustion chamber and a more complete combustion process. The more complete combustion process, in turn, reduces the level of undesirable emissions.
Spray penetration and dispersion are also critical factors which must be controlled in order to ensure an efficient DI system. Spray penetration is controlled to prevent undesirable wetting of the combustion chamber wall with fuel. Any fuel that wets the combustion chamber wall is not likely to evaporate into suspension with the combustion charge. Thus, the combustion process is likely to be incomplete and to result in increased levels of undesirable emissions. Spray dispersion determines levels at which fuel is concentrated within various parts of the combustion chamber. As stated above, uncontrolled localized high concentrations of fuel within the combustion chamber are undesirable as they may result in an incomplete combustion process and higher levels of undesirable emissions. However, under certain operating conditions, controlled and targeted localized high concentrations of fuel within the combustion chamber, such as, for example, proximate the spark plug, are desirable. The purposeful creation of targeted localized high concentrations of fuel is known as stratification of the combustion charge, and is central to realizing the benefits of increased fuel economy and reduced emissions in a DI system. Stratification of the combustion charge enables an engine to operate with a very lean overall combustion charge, even under partial load conditions.
Conventional DI systems atomize fuel by flowing the fuel under pressure through the nozzle of a fuel injector and into the combustion chamber. As the pressure is increased, the atomization of the fuel increases and particle size is reduced. In order to achieve sufficiently small fuel particle size, conventional DI systems require the fuel to flow through the nozzle under relatively high pressure, such as, for example, from 5 to 12 MPa. Although these high pressures may achieve adequate fuel atomization, the injected fuel has a correspondingly high spray front velocity, such as, for example, above forty meters per second. With such high spray front velocities, it is difficult to achieve desirable levels of spray penetration and spray dispersion. Thus, fuel is likely to be impinged upon the combustion chamber wall and/or highly and uncontrollably dispersed within the combustion chamber. In fact, due to the high operating pressures required to adequately atomize fuel and the resulting high spray front velocities, many conventional DI systems must impinge fuel off the combustion chamber wall and/or the piston to create a stratified combustion charge. Furthermore, conventional DI systems require a high-pressure fuel pump and high-pressure fuel rails thereby adding complexity, weight, and cost to the DI system. Moreover, the nozzle of the fuel injector must be machined to exacting tolerances, making the nozzle difficult to manufacture, sensitive to manufacturing variations, and costly to procure.
Advanced DI systems may include nozzles constructed with synthetic materials and/or advanced machining processes. For example, advanced nozzles may be compound structures including two or more elements which are bound together. Such advanced nozzles may further include several inlet orifices and a single outlet orifice. However, such compound nozzles require multiple machining operations upon each element. Further, the elements must then be precisely aligned and bonded together. Thus, such advanced nozzles require relatively large amounts of materials and multiple processing. Moreover, such nozzles typically include relatively high, and thus undesirable, sac volume. Sac volume is the volume of fluid that, due to surface tension, clings to an outlet orifice of a nozzle after flow is ceased. In the context of DI systems, the sac volume is a volume of non-atomized fuel which, upon the next injection event, is injected into the combustion chamber. This non-atomized volume of fuel is not metered or controlled, nor does it disperse well or evaporate quickly within the combustion chamber. As a result of a relatively high sac volume, the level of undesirable emissions are increased and fuel economy is decreased. Compound nozzles have a relatively high sac volume since the non-atomized fuel will cling to the walls of the multiple orifices formed in each element.
Therefore, what is needed in the art is a pressure atomizer which efficiently atomizes fuel under substantially lower pressure than conventional fuel atomizer nozzles to thereby eliminate the need for high-pressure components, such as, for example, a high-pressure fuel pump.
Furthermore, what is needed in the art is a pressure atomizer that enables stratification of the combustion charge, control of spray dispersion and spray penetration.
Still further, what is needed in the art is a pressure atomizer that substantially reduces spray velocities to thereby improve control of spray dispersion, spray penetration, and stratification of the combustion charge.
Even further, what is needed in the art is a pressure atomizer that achieves small fuel droplet size and low spray penetration to thereby increase fuel economy and decrease undesirable emissions.
Yet further, what is needed in the art is a pressure atomizer that minimizes sac volume.
Moreover, what is needed in the art is a single element, or non-compound, pressure atomizer that eliminates machining multiple elements and the process of bonding the elements together.
The present invention provides a pressure atomizer for use in fuel injection systems.
The invention comprises, in one form thereof, a silicon plate having a top surface and a bottom surface. A portion of the top surface defines a turbulent chamber. The turbulent chamber is peripherally bounded by the top surface of the plate. The turbulent chamber is recessed a predetermined distance relative to the top surface. The silicon plate further defines at least one flow orifice. Each flow orifice extends from the bottom surface of the silicon plate to intersect with and open into the turbulent chamber. Each flow orifice is in fluid communication with the turbulent chamber.
An advantage of the present invention is that fuel is substantially completely atomized in an efficient manner and at substantially lower pressure than in conventional pressure atomizer nozzles.
Another advantage of the present invention is that the need for high-pressure components, such as, for example, a high-pressure fuel pump, are eliminated.
A still further advantage of the present invention is that the sac volume of fuel is substantially reduced over conventional compound pressure atomizer nozzles.
An even further advantage of the present invention is that spray front velocities are substantially reduced to thereby improve spray dispersion, spray penetration, and stratification of the combustion charge.
Lastly, an advantage of the present invention is that a single silicon plate is used, thereby eliminating the need to machine multiple nozzle elements and to bond the elements together.